Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

An electrostrictive composite includes a flexible polymer matrix, a
plurality of carbon nanotubes and a plurality of reinforcing particles
dispersed in the flexible polymer matrix. The carbon nanotubes
cooperatively form an electrically conductive network in the flexible
polymer matrix.

Claims:

1. An electrostrictive composite comprising: a flexible polymer matrix;
and a plurality of carbon nanotubes and a plurality of reinforcing
particles dispersed in the flexible polymer matrix, the carbon nanotubes
cooperatively forming an electrically conductive network in the flexible
polymer matrix, wherein a weight percentage of the sum of the carbon
nanotubes and reinforcing particles in the electrostrictive composite is
less than 20%.

2. (canceled)

3. The electrostrictive composite of claim 1, wherein a weight ratio of
the carbon nanotubes to the reinforcing particles is greater than or
equal to 1:1.

4. The electrostrictive composite of claim 1, wherein a weight percentage
of the reinforcing particles in the electrostrictive composite ranges
from about 1% to about 10%.

5. The electrostrictive composite of claim 1, wherein the reinforcing
particles are made of material selected from a group consisting of
ceramic, metal, metal oxide, metal nitride, glass and combinations
thereof.

6. The electrostrictive composite of claim 1, wherein an effective
diameter of the reinforcing particles ranges from about 1 nanometer to
about 10 micrometers.

7. The electrostrictive composite of claim 1, wherein a weight percentage
of the carbon nanotubes in the electrostrictive composite ranges from
about 0.1% to about 10%.

8. The electrostrictive composite of claim 1, wherein the carbon
nanotubes are selected from a group consisting of single-walled carbon
nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes,
and combinations thereof.

10. The electrostrictive composite of claim 1, further comprising at
least one flexible polymer layer located on one surface of the flexible
polymer matrix.

11. The electrostrictive composite of claim 10, wherein the flexible
polymer matrix is located between two flexible polymer layers.

12-19. (canceled)

20. An electrostrictive composite comprising: a flexible polymer matrix;
and a plurality of carbon nanotubes and a plurality of reinforcing
particles dispersed in the flexible polymer matrix, and the carbon
nanotubes cooperatively forming an electrically conductive network in the
flexible polymer matrix, wherein the reinforcing particles are made of
material selected from a group consisting of ceramic, metal, metal oxide,
metal nitride, glass and combinations thereof.

21. An electrostrictive composite comprising: a flexible polymer matrix;
and a plurality of carbon nanotubes and a plurality of reinforcing
particles dispersed in the flexible polymer matrix, and the carbon
nanotubes cooperatively forming an electrically conductive network in the
flexible polymer matrix, wherein an effective diameter of the reinforcing
particles ranges from about 1 nanometer to about 10 micrometers.

Description:

RELATED APPLICATIONS

[0001] This application is related to copending applications entitled
"ELECTROSTRICTIVE COMPOSITE AND METHOD FOR MAKING THE SAME", filed ______
(Atty. Docket No. US22230); and "ELECTROSTRICTIVE MATERIAL METHOD FOR
MAKING THE SAME AND ELECTROTHERMIC TYPE ACTUATOR", filed ______ (Atty.
Docket No. US22892). The disclosures of the above-identified applications
are incorporated herein by reference.

BACKGROUND

[0002] 1. Technical Field

[0003] One disclosure relates to a carbon nanotube based electrostrictive
composite and method for making the same.

[0004] 2. Description of Related Art

[0005] Electrostrictive composites are materials that can convert
electrical energy to mechanical energy, thus imparting a force, while a
current or voltage is applied. Electrostrictive composites have been
called artificial muscles due to their similar motion properties.

[0006] Referring to FIG. 6, a flexible electrothermal composite 10
according to a prior art is shown. The flexible electrothermal composite
10 includes a flexible polymer matrix 14 and a plurality of carbon
nanotubes 12 dispersed therein. The carbon nanotubes 12 cooperatively
form a conductive network in the flexible polymer matrix 14. The flexible
electrothermal composite 10 is made by the following steps of: (a)
preparing a solution of a polymer precursor; (b) immersing carbon
nanotubes in the solution and ultrasonically cleaning the solution; and
(c) polymerizing and curing the polymer precursor.

[0007] However, the Young's modulus of the flexible electrothermal
composite 10 is relatively small.

[0008] What is needed, therefore, is to provide an electrostrictive
composite having a relatively larger Young's modulus and method for
making the same.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Many aspects of one electrostrictive composite and method for
making the same can be better understood with reference to the following
drawings. The components in the drawings are not necessarily drawn to
scale, the emphasis instead being placed upon clearly illustrating the
principles of one electrostrictive composite and method for making the
same.

[0010] FIG. 1 is a schematic view of an electrostrictive composite.

[0011] FIG. 2 is a schematic view of the electrostrictive composite of
FIG. 1 before and after expansion.

[0012] FIG. 3 is a schematic view of an electrostrictive composite having
a sandwich structure.

[0013] FIG. 4 is a schematic view of an electrostrictive composite having
a multi-layer structure.

[0014] FIG. 5 is a flow chart of a method for making the electrostrictive
composite of FIG. 1.

[0015] FIG. 6 is a schematic view of a flexible electrothermal composite
according to the prior art.

[0016] Corresponding reference characters indicate corresponding parts
throughout the several views. The exemplifications set out herein
illustrate at least one embodiment of one electrostrictive composite and
method for making the same, in at least one form, and such
exemplifications are not to be construed as limiting the scope of the
disclosure in any manner.

DETAILED DESCRIPTION

[0017] References will now be made to the drawings to describe, in detail,
various embodiments of one electrostrictive composite and method for
making the same.

[0018] Referring to FIG. 1, an electrostrictive composite 20 according to
one embodiment is shown. The electrostrictive composite 20 includes a
flexible polymer matrix 22, a plurality of carbon nanotubes 24, and a
plurality of reinforcing particles 26. The carbon nanotubes 24 and
reinforcing particles 26 are dispersed in the flexible polymer matrix 22.
Shape and size of the electrostrictive composite 20 are arbitrary. In one
embodiment, the electrostrictive composite 20 is rectangular, and the
carbon nanotubes 24 and the reinforcing particles 26 are uniformly
dispersed in the flexible polymer matrix 22.

[0019] A weight percentage of the flexible polymer matrix 22 in the
electrostrictive composite 20 ranges from about 80% to about 98.9%. The
flexible polymer matrix 22 includes a material selected from a group
consisting of silicone elastomer, polyester, polyurethane, epoxy resin,
polymethyl methacrylate (PMMA) and combinations thereof. In one
embodiment, the flexible polymer matrix 22 is silicone elastomer.

[0020] A weight percentage of the sum of the carbon nanotubes 24 and
reinforcing particles 26 in the electrostrictive composite 20 is less
than 20%. A weight ratio of the carbon nanotubes 24 to the reinforcing
particles 26 is greater than or equal to 1:1. A weight percentage of the
reinforcing particles 26 in the electrostrictive composite 20 can range
from about 1% to about 10% and a weight percentage of the carbon
nanotubes 24 in the electrostrictive composite 20 can range from about
0.1% to about 10%. In one embodiment, a weight percentage of the
reinforcing particles 26 in the electrostrictive composite 20 ranges from
about 1% to about 5% and a weight percentage of the carbon nanotubes 24
in the electrostrictive composite 20 ranges from about 0.1% to about 5%.

[0021] The carbon nanotubes 24 can be selected from a group consisting of
single-walled carbon nanotubes, double-walled carbon nanotubes,
multi-walled carbon nanotubes, and combinations thereof. A length of the
carbon nanotubes 24 can be greater than about 1 micrometer. The length of
the carbon nanotubes 24 can range from about 50 micrometers to about 900
micrometers in one embodiment. The carbon nanotubes 24 are flexible and
have excellent electricity to heat conversion efficiency. The carbon
nanotubes 24 are in contact with each other to form a conductive network
in the flexible polymer matrix 22, thus the electrostrictive composite 20
is conductive. While a voltage is applied to the electrostrictive
composite 20, the carbon nanotubes conductive network will rapidly heat
and expand the flexible polymer matrix 22.

[0022] The reinforcing particles 26 can be made of material selected from
a group consisting of ceramic, metal, metal oxide, metal nitride, glass
and combinations thereof. An effective diameter of the reinforcing
particles 26 can range from about 1 nanometer to about 10 micrometers.
The reinforcing particles 26 can reduce the thermal response time of the
electrostrictive composite 20 due to its high thermal conductivity. The
reinforcing particles 26 can enhance the Young's modulus of the
electrostrictive composite 20 and raise its propelling power capability
during expansion.

[0023] Testing was performed on the electrostrictive composite 20 wherein
the flexible polymer matrix 22 was silicone elastomer with a weight ratio
of 94 wt %, the carbon nanotubes 24 were multi-walled carbon nanotube
with a weight ratio of 4 wt %, and the reinforcing particles 26 were
boron nitride (BN) particles with a weight ratio of 2 wt %. The Young's
modulus of the electrostrictive composite 20 was 1.92 MPa. In another
test, the flexible polymer matrix 22 was silicone elastomer with a weight
ratio of 94 wt %, the carbon nanotubes 24 were multi-walled carbon
nanotube with a weight ratio of 4 wt %, and the reinforcing particles 26
were aluminum oxide (Al2O3) particles with a weight ratio of 2
wt %. The Young's modulus of the electrostrictive composite 20 was 1.57
MPa. Another test found that the Young's modulus of a composite
consisting of silicone elastomer of 96 wt % and carbon nanotubes of 4 wt
% was 1.2 MPa.

[0024] The work principle of the electrostrictive composite 20 is
described as follows. When a voltage is applied to the electrostrictive
composite 20, a current flows through the carbon nanotube conductive
network. The electrical energy absorbed by the carbon nanotubes 24
results in local thermal confinement, which breaks the thermodynamic
equilibrium therearound. The current and temperature increase
simultaneously and rapidly until another thermodynamic equilibrium is
achieved. The temperature of the carbon nanotubes 24 rises by absorbing
electrical energy, resulting in a temperature increase of the flexible
polymer matrix 22 due to the high thermal conductance of the carbon
nanotubes. That can lead to an expansion of the electrostrictive
composite 20 along its length and width.

[0025] The expansion coefficient of the electrostrictive composite 20
ranges from about 0.66×10-4K-1 to about
5.28×10-4K-1. Referring to FIG. 2, in one embodiment, the
expansion coefficient of the electrostrictive composite 20 is tested. In
the tested electrostrictive composite 20, the flexible polymer matrix 22
is silicone elastomer of 91 wt %, the carbon nanotubes 24 are
multi-walled carbon nanotube of 5 wt %, and the reinforcing particles 26
are Al2O3 particle of 4 wt %. An effective diameter of the
reinforcing particles 26 ranges from about 10 nanometers to about 100
nanometers. The expansion coefficient α of the electrostrictive
composite 20 is calculated according to

α = L 2 - L 1 L 1 × 1
Δ T = Δ T ##EQU00001##

[0026] where L1 is the original length of the electrostrictive composite
20, L2 is the length of the electrostrictive composite 20 after
expansion, ΔT is the increase of the temperature of the
electrostrictive composite 20, ε is the strain. In one
embodiment, the L1 is 4 millimeters. The L2 increases to 4.2 millimeters
after a voltage of 40 V is supplied for about 2 minutes. The increase of
the length ΔL is 0.2 millimeters. The increase of the temperature
ΔT is 150K. The strain ε of the electrostrictive composite
20 is calculated to be is the 5%. The expansion coefficient α of
the electrostrictive composite 20 is calculated to be
3.3×10-4K-1.

[0027] In other embodiments, the electrostrictive composite 20 can further
include at least one flexible polymer layer 28 located on at least one
surface of the flexible polymer matrix 22. The electrostrictive composite
20 with the flexible polymer layer 28 on at least one surface of the
flexible polymer matrix 22 can be an insulator. A thickness ratio of the
flexible polymer layer to the flexible polymer matrix 22 can range from
about 1% to about 10%. In one embodiment, the flexible polymer matrix 22
can be sandwiched between two silicone elastomer layers serving as the
flexible polymer layers 28 as shown in FIG. 3. Alternatively, the
electrostrictive composite 20 can be a multi-layer structure as shown in
FIG. 4.

[0028] Referring to FIG. 6, a method of making the electrostrictive
composite 20 includes the following steps of: (a) providing a plurality
of carbon nanotubes, a plurality of reinforcing particles and a polymer
precursor; (b) mixing the carbon nanotubes, reinforcing particles and the
polymer precursor to obtain a mixture; and (c) polymerizing and curing
the polymer precursor in the mixture.

[0029] In step (a), the carbon nanotubes can be obtained by a conventional
method selected from a group consisting of chemical vapor deposition
(CVD), arc discharging, and laser ablation. In one embodiment, the carbon
nanotubes are obtained by the following substeps of: providing a
substrate; forming a carbon nanotube array on the substrate by a chemical
vapor deposition method; peeling the carbon nanotube array off the
substrate by a mechanical method, thereby achieving a plurality of carbon
nanotubes. The carbon nanotubes in the carbon nanotube array can be
substantially parallel to each other.

[0030] The reinforcing particles can be made by a sol-gel or ball milling
process. The polymer precursor can be selected according to the flexible
polymer. The polymer precursor generally includes a prepolymer or a
monomer. The prepolymer can be selected from the group consisting of
silicone elastomer prepolymer, polyester prepolymer, polyurethane
prepolymer, epoxy resin prepolymer, PMMA prepolymer and combination
thereof. In one embodiment, the flexible polymer is silicone elastomer,
and the prepolymer is silicone elastomer prepolymer.

[0031] In step (b), when the polymer precursor is liquid, the carbon
nanotubes and reinforcing particles can be added into the polymer
precursor directly to obtain a liquid mixture. When the polymer precursor
is solid or glue-like, step (b) can include the substeps of: (b1)
dissolving the polymer precursor into a volatilizable solvent to obtain a
solution of polymer precursor; and (b2) adding the carbon nanotubes and
the reinforcing particles into the solution to obtain a liquid mixture.
In one embodiment, the component A of the silicone elastomer is dissolved
into ethyl acetate. The component A can be hydroxyl terminated
polydimethylsiloxane.

[0032] After step (b), an optional step (d) of ultrasonically treating the
liquid mixture can be carried out. In step (d), ultrasonically treatment
of the liquid mixture is performed in an ultrasonic processor for about
10 minutes to reduce the size of the carbon nanotubes and reinforcing
particles. In order to avoid the carbon nanotubes conglomerating with
each other in the solution, step (d) further includes the following steps
of: ultrasonically agitating the solution for a few minutes to uniformly
disperse the carbon nanotubes therein. In one embodiment, ultrasonic
agitation is performed in an ultrasonic cleaner for about 3 hours.

[0033] When the polymer precursor is dissolved into a volatilizable
solvent, an optional step (e) of removing the volatilizable solvent can
be performed before the step (c). In one embodiment, the liquid mixture
is heated in an oven at a temperature ranging from about 80° C. to
about 120° C. until all the ethyl acetate is volatilized.

[0034] In step (c), the polymer precursor is polymerized with an initiator
to obtain a flexible polymer matrix having carbon nanotubes and
reinforcing particles dispersed therein. In one embodiment, the initiator
includes a solution of ethanol or deionized water having component B of
the silicone elastomer dispersed therein. The initiator is added in the
solution of the prepolymer having component A of the silicone elastomer
to obtain a mixture solution, in order to polymerize the prepolymer. A
weight ratio of the initiator and the prepolymer can be about 6:100. In
one embodiment, the component A can be hydroxyl terminated
polydimethylsiloxane and the component B can be tetraethoxysilane. Then,
after ultrasonically agitating the mixture solution, sediment is
collected. The sediment (a glue-like material) having the carbon
nanotubes and the reinforcing particles uniformly dispersed therein is
the electrostrictive composite.

[0035] An optional step (f) of keeping the electrostrictive composite in a
vacuum for a period of time to remove bubbles therein can be carried out
after step (c). An optional step (g) of pressing the electrostrictive
composite can be carried out to obtain a smooth electrostrictive
composite after step (f). In one embodiment, the electrostrictive
composite is pressed by a smooth presser for about 12 hours to about 18
hours to obtain a planar electrostrictive composite. Furthermore, the
planar electrostrictive composite can be cut to have a rectangular shape.

[0036] In addition, a step (h) of forming a flexible polymer layer on at
least one surface of the flexible polymer matrix can be carried out after
step (g). Step (h) can include the substeps of: (h1) providing a liquid
prepolymer; (h2) adding initiator into the liquid prepolymer to obtain a
liquid mixture; and (h3) immersing the electrostrictive composite into
the liquid mixture.

[0037] It is also to be understood that the above description and the
claims drawn to a method may include some indication in reference to
certain steps. However, the indication used is only to be viewed for
identification purposes and not as a suggestion as to an order for the
steps.

[0038] Finally, it is to be understood that the above-described
embodiments are intended to illustrate rather than limit the disclosure.
Variations may be made to the embodiments without departing from the
spirit of the disclosure as claimed. The above-described embodiments
illustrate the scope of the disclosure but do not restrict the scope of
the disclosure.